As the most key technique in medical ultrasound diagnosis systems, the quality of the beamforming has significant effect on the accuracy and resolution of ultrasound imaging. Most of ultrasound imaging systems have their focusing parameters stored in RAMs within the systems, which ask for a huge number of memories, especially when it is needed to support line array keystone scanning and phased arrays. For example, where a system utilizes a sample of 30 M, a probe depth of 30 cm and the receive focus is shifted every 8 timing clock, if all the receive parameters are to be pre-stored, excessive 200 Mbytes have to be taken up thereby. The increase of memories will necessarily lead to the systems being expensive in fabrication and slow in loading parameters when a probe is switched over.
A solution is to use a real-time parameter calculation hardware. Whereby, as the ultrasound imaging takes a scanning line as the basic unit, storage of a few parameters and a write-in of several control meters before the reception of each scanning line transmission enable the hardware to automatically generate the focusing parameters desired during reception. Thus, memory resources may be significantly saved.
U.S. Pat. No. 6,110,116 provides a focusing method in the course of beamforming by pre-storing delay data. Specifically, the focus data are pre-stored and the echoes of each focusing area use corresponding pre-stored focus data. While this method is simple and convenient, a larger memory is needed and further, many parameters need to be reloaded at the time of changing the probe. Thus, the speed of startup and the switchover of the probe is affected.
U.S. Pat. No. 6,123,671 provides a CORDIC-based method for real-time calculation of receive focus and apodization parameters, which is applicable for various geometrical probes including two-dimensional probes, and for multiple beams. The basic idea of this method is to calculate the delay differences of each array element corresponding to different receive focuses and take the delay differences as the parameters to control the beamforming. Although the method of U.S. Pat. No. 6,123,671 is simple and efficient as well as occupies fewer hardware resources, its circuit is rather complex.
In contrast, the present invention calculates the receive focusing parameters by way of directly calculating the reading address of the memory storing AD conversion data of each channel, instead of calculating delay differences of each array element of the probe. Thus, the circuit is much simpler than that of U.S. Pat. No. 6,123,671. Furthermore, since a real-time calculation is adopted to calculate the receive focus coordinates which thereby do not have to be pre-stored more memory resources may be saved and at the same time, the beam correction may be accomplished.